BIOLOGY: Photosynthesis

What is photosynthesis?
Photosynthesis is a process employed by plants and other organisms to convert light energy from the sun into chemical energy which is then used to power the organism's activities. This name was proposed by Barnes in 1898. Photosynthesis is derived from two words, 'photo' meaning 'light' and 'synthesis' meaning 'building up'. It consists in the building up of simple carbohydrates (sugars), in the green leaf  of plants or green part of organism containing chloroplasts in the presence of sunlight from carbon dioxide absorbed from the air and water absorbed from soil.

The volume of oxygen given off has been found to be equal to the volume of carbon dioxide absorbed. Moreover, the oxygen liberated is released from water and not from Carbon dioxide. The oxygen evolved escapes from the plant body through stomata.


 Equation of Reaction

 

Mechanism of photosynthesis
Photosynthesis is essentially an Oxidation-Reduction process by which hydrogen is transferred from water to Carbon dioxide through a carrier substance. Photosynthesis involves two distinct phases which includes;

• Light-phase Reactions or Light-dependent Phase
• Dark-phase Reactions or Light-Independent Phase 

Light-phase: These reaction takes place in the green cells of plant (Grana) in the presence of light. Chlrophyll absorbs light energy and converts it into chemical energy which is temporarily stored in two compounds, Adenosine Triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADP.H₂). Photolysis of water takes place in this stage and water supplies hydrogen ions used to reduce NADP to NADPH₂. This NADPH₂ serves as the reducing power used to reduce CO₂ to glucose. The light Phase is divided into

• Cyclic Photophosphorylation and
• Non-cyclic photophosphorylation

Dark-phase: This process utilizes the  potential chemical energy stored in green cells during light reactions. It occurs in the Stroma of the chlroplast. The first step of this reaction is carbon dioxide fixation. The light-independent phase involves series of processes to reduce CO₂ to glucose.


Factors affecting photosynthesis

1. Light
2. Carbon  dioxide
3. Temperature
4. Water
5. Chlorophyll
6. Accumulation of photosynthetic products

Importance of Photosynthesis

1. Photosynthesis converts inorganic raw materials into food, that provides the ecosystem with energy i.e Green plants provide organic food to all the animals and human
2. Photosynthesis helps in providing oxygen in the atmosphere required by all living organisms.
3. Photosynthesis decreases the concentration of carbon dioxide and other harmful industrial wastes that lead to respiratory problems in living organisms. 

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